Conventionally, there has been a brushless DC motor excluding physical contact of a brush by detecting a position of a magnet of a rotor with a hall element magnetic sensor and controlling energization to a coil with an electronic circuit. As for such a brushless DC motor, Non-patent document 1 provides, on page 91, a circuit diagram of a drive circuit shown in FIG. 15A. The circuit of this dual-phase bidirectional energization drive type brushless DC motor comprises two hall elements 202 at both inputs of two dual-phase push-pull circuits, which are arranged with their phase positions offset. By detecting the position of the rotor by respective hall elements 202, the energization to respective drive coils 201 arranged with their phases shifted may be controlled.
On the other hand, Patent document 1 describes, as shown in FIG. 15B, a circuit comprising a rotor 1 having permanent magnets magnetized to have N and S magnetic poles; a detecting coil 3; a drive coil 2; and a transistor 5 controlling a drive current, wherein electromotive force of the detecting coil 3 controls the drive current to the drive coil 2.